How Cold Is Too Cold for a Heat Pump? What the Makers Say

By Ray Bennett · Updated 2 October 2026 · 5 min read · Checked against the sources at the end

How Cold Is Too Cold for a Heat Pump? What the Makers Say

Short answer

It depends on the heat pump. Trane says the best standard heat pumps still give full heating capacity at about 32°F, and most standard ones will not run at all much below 0°F. A heat pump with ENERGY STAR's cold climate mark must still give at least 70 percent of its capacity at 5°F. Mitsubishi guarantees its Hyper-Heating models run at -13°F, and Carrier says its 27VNA1 heats at -23°F.

How cold is too cold for a heat pump? There is no single number, because it depends on the heat pump. Trane calls it a myth that heat pumps do not work in cold weather, but says they become less efficient below freezing, and that most standard heat pumps will not run at all much below 0°F.

Cold climate heat pumps are built for the rest of the thermometer. This page shows how far each kind goes, the rating that tells them apart, and what the backup heat does on the coldest days.

Before you start

What to carry: a torch and a pen, to copy the model number off the outdoor unit and note the outdoor temperature. Five minutes.

Gas or electric? The heat pump runs on electricity. Its backup can be electric strips or a gas furnace, and which one you have changes what happens on the coldest nights.

Find out which kind you have. ENERGY STAR requires a heat pump that meets its cold climate criteria to carry a separate cold climate mark in its literature. Search the model number for it.

What the makers are clear about. Below freezing, it works harder. Trane says a standard heat pump near freezing has to work harder to bring heat in, which can drive up the bills.

Emergency heat is not a winter setting. Google says emergency heat has to be switched on by hand and is usually expensive and inefficient to run. Needing it regularly means the heat pump may need service.

The rating point is 47°F. ENERGY STAR takes a heat pump’s nominal heating capacity at 47°F. On a colder night it gives less, and the cold climate test checks how much less at 5°F. What that means for choosing a size: what size heat pump do I need.

How cold each kind can go

What each maker says its heat pumps do as the temperature falls, with ENERGY STAR's cold climate test at 5°F.

Check 1Free, five minutes

Place your heat pump on the scale

A standard heat pump. Trane says the most efficient ones give 100 percent of their heating capacity down to about 32°F and then may start losing it. Trane’s best current model in the cold heats at 5°F with a 70 percent capacity ratio there.

A cold climate heat pump. To carry ENERGY STAR’s cold climate mark, a heat pump must keep at least 70 percent of its 47°F capacity at 5°F, reach a COP of 1.75 there, and pass a check that its own controls actually deliver that in a home.

Mitsubishi. It says its Hyper-Heating systems give 100 percent of rated capacity as low as 5°F with operation guaranteed down to -13°F, and its H2i plus models hold 100 percent down to -5°F.

Carrier and Trane’s newest. Carrier says its 27VNA1 heats down to -23°F without a loss of heating power. A Trane product manager says its cold climate heat pumps hold maximum capacity down to 0°F and keep heating as low as -10 to -20°F.

What the ratings mean

Check 2

Read COP and HSPF2

COP. ENERGY STAR defines it as the heat delivered divided by the electricity used. At ENERGY STAR’s cold climate floor of 1.75, a heat pump still gives out 1.75 units of heat for each unit of electricity at 5°F.

At its best. Trane says a heat pump can be up to 300 percent efficient in the right conditions, three times the heat for the energy it uses.

HSPF2. Trane says that if cold weather performance matters, look for a higher HSPF2. ENERGY STAR’s cold climate mark needs at least 8.1 for a ducted split system and 8.5 for a ductless one.

Against electric heat. Carrier says an electric furnace uses more electricity than a heat pump for the same heat. Trane quotes the Department of Energy: a heat pump can cut electricity for heating by about 75 percent against electric furnaces or baseboard heat.

The backup heat on the coldest days

Three ways a heat pump house stays warm when it is coldest. Which one you have decides what the bill does.

Check 3Free to check

Know what takes over, and when

Dual fuel. Trane says the gas furnace takes over when the temperature drops below freezing for a standard heat pump, and below 5°F for its cold climate models. Carrier says its Greenspeed heat pumps can run down to -15°F before switching to the furnace.

Electric strips. These are the aux heat. Google says aux heat comes on when it is too cold outside or during defrost, below the lockout temperature set in the thermostat: aux heat on the thermostat.

A thermostat set too high. Google says a big jump in the set temperature can bring aux heat on too, so small steps keep more of the work on the heat pump.

What is normal on a cold day

Check 4

Tell normal cold weather running from a fault

Air that feels cool. Heat pump air is cooler than a furnace’s even when all is well. Measure it before worrying: a heat pump that is not heating.

Long runs. On the coldest days a heat pump may run for long stretches: a heat pump that runs constantly.

Frost, steam and a pause. A defrost cycle is normal, a block of ice is not: a heat pump frozen in winter.

Questions people ask

At what temperature does a heat pump stop working?

Trane says most standard heat pumps will not run at all much below 0°F. Cold climate models go lower: Mitsubishi guarantees -13°F on its Hyper-Heating systems and Carrier says -23°F on its 27VNA1.

Do heat pumps work below freezing?

Yes, but less efficiently. Trane says the best standard heat pumps give full capacity down to about 32°F and then may start losing it.

What is a cold climate heat pump?

One built to keep heating well below freezing. ENERGY STAR’s cold climate mark requires at least 70 percent of rated capacity and a COP of 1.75 at 5°F.

Should I switch to emergency heat when it is very cold?

No. Google says emergency heat is switched on by hand and is usually expensive and inefficient. Aux heat comes on by itself when it is needed.

Can a heat pump heat a house in a cold climate on its own?

A cold climate model can. Carrier says many homeowners in cold regions replace furnaces with them, and that dual fuel adds a furnace as backup for the coldest days.

Why does my heat pump run all day when it is cold?

The colder it gets, the harder it works to bring heat in. Long runs on the coldest days can be normal, and the aux heat helps below its lockout temperature.

Sources: Trane "At What Temperature Do Heat Pumps Stop Working?" and "What Is a Dual Fuel Heat Pump System?", the ENERGY STAR Version 6.2 Central Air Conditioner and Heat Pump specification, Mitsubishi Electric "Heat Pumps in Extreme Cold Climates", Carrier "Cold Climate Heat Pump Systems" and "Heat Pump vs Furnace", and Google Nest Help "Heat Pump Balance" and "Emergency Heat for heat pump systems"